The present invention relates to display systems, and more particularly, to a method for providing a marker on a peak of interest in a signal display such as that provided with spectrum analyzers and the like.
Spectrum analyzers provide a display which tracks the amplitude versus frequency of the various frequency components of a signal input thereto. The displayed portion of the signal spectrum typically includes a number of peaks corresponding to different signal frequencies. The peaks often move over time and change amplitude. In many cases, the spectrum analyzer user needs to follow one of these peaks as it moves back and forth on the display screen (i.e. changes frequency) without otherwise altering the display. Prior art display systems for spectrum analyzers do not provide this functionality.
Broadly, it is the object of the present invention to provide an improved display system for a spectrum analyzer.
It is a further object of the present invention to provide a marker that appears on the display screen at the location of a peak of interest and moves with that peak.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a method for operating a spectrum analyzer to provide a marker that follows a peak from sweep to sweep in a spectrum display. The spectrum display includes a graph of the amplitude of a signal plotted against frequency. The present invention operates on first and second measured spectrums. The first measured spectrum includes a plot of the signal amplitude against frequency during a first time interval in which the marker has been assigned a first frequency and first amplitude corresponding to the peak of interest. The second spectrum includes a plot of the signal amplitude against frequency during a subsequent time interval in which the marker is to be assigned a new frequency and amplitude location. The present invention begins by defining a first frequency range in the second measured spectrum centered around the first frequency. The first frequency range is searched for a candidate peak having an amplitude within a first range centered on the first amplitude. If such a candidate peak is found, the marker location is assigned to the frequency of the candidate peak in the second spectrum and the amplitude of the marker to the amplitude of the candidate peak in the second spectrum. If more than one such candidate peak is found by the search, the frequency and amplitude of the candidate peak closest to the first frequency are assigned as the marker location. If a candidate peak is not found, a second frequency range is defined in the second measured spectrum centered around the first frequency. The second frequency range is then searched for a candidate peak having an amplitude within a second range centered on the first amplitude. If such a candidate peak is found, the marker location is assigned to the frequency of the candidate peak in the second spectrum and the amplitude of the marker to the amplitude of the candidate peak in the second spectrum. If more than one such candidate peak is found by the search, the frequency and amplitude of the candidate peak farthest from the first frequency are assigned as the marker location. If no candidate peak is found, a third frequency range in the second measured spectrum is defined and this frequency range is searched for candidate peaks. The third frequency range preferably includes the entire measured frequency range. The candidate peaks found are assigned an order value based on the differences in frequency and amplitude between each candidate peak and the first frequency and the first amplitude, respectively. The marker location is assigned to the frequency and amplitude of the candidate peak having the highest order value. The order value preferably depends on a weighted sum of difference in frequency and the difference in amplitude.